I am so sorry that you are feeling this way. It is natural to feel envious of the people that got to go to the Bahamas. But there is always next year. Please don't feel worthless or stupid because you are neither. You made some mistakes and now you are starting fresh. It isn't easy. I know. Don't let your mom get to you. She wants you to feel guilty, so that you have learned your lesson in her eyes. But that isn't how it really is. We all make mistakes. Just try to focus on what you are doing in class. I think you have a lot on your mind and it is hard to pay attention to what you are doing. Try to keep your mind in the now. It is hard, but can be done.
One of the worse things that you could do is compare yourself to other people. We are all built differently and you aren't over weight. It sounds like she is kind of skinny to me. But that is my opinion. Try to focus on school, if you want to be able to do all the things that they are doing you need to study so that you can. If you choose to drink that is your decision, but it wont take your problems away. They will still be there and you will probably feel more guilty than you do now afterwards. So be careful.
Just remember when you go back to the other school in the fall, you will meet new people and I think that you will enjoy the experience. So it wont be all that bad. You will make it Confused, I know that you will.
In the meantime we are here for you. And you know that you can email me whenever you feel the need.